This invention relates to helicopters, and more particularly to the provision of a fixed leading edge slat/spoiler mounted on horizontal stabilizers to optimize stabilizer performance for the high aerodynamic angle of attack range and also to act as a spoiler for descending flight to reduce the stabilizer lift capability.
Horizontal stabilizers are provided on helicopters and are either of the fixed or controllable type. In the maneuvering of helicopters when in high power climb, it is desired to maintain a high downlift by the horizontal stabilizer. At high inflow angles to the rotor disk, as in high power climb, the damping moment of the rotor decreases thereby reducing the rotor stability. Under such conditions, high downlift from the stabilizer is highly desirable in order to retain fuselage stability. During descent, the rotor has a greater damping moment and is more stable. It is then possible to reduce the stabilizer contribution to airframe stability by stalling the stabilizer to reduce the uplift it provides. At the same time, it is desired to maintain the necessary construction in as simple a form as possible.
It has been found that by suitably applying slats to the stabilizer, a fixed stabilizer can be employed thereby eliminating control surfaces for such stabilizer and at the same time substantially increasing the permissible range for the negative angle of attack without stall. It has been the experience that in high power climbs the stabilizer will stall out, thus eliminating the downlift generated thereby. In such case, the tail of the helicopter comes up and the motion of the ship as it moves through the air is somewhat akin to that of a porpoise through water. With application of instrument flight controls, it is still further necessary to minimize the undesired motions of the aircraft. The present invention provides for operation of the stabilizer in a manner to enhance the flight characteristics of the aircraft with minimum of structure.